LONDON/KUWAIT ( Reuters ) - The drop Movement.down.loss in oil prices to their weakest level Position.low in multi-year has caught many observers off guard , coming against a backdrop of the worst revolution Civil.unrest in Iran this decade , heightened clashes Geopolitical.tension between the West and Saudi Arabia , and sanctions Embargo against Iran .

Three decades ago , the spike Movement.up.gain in prices caused by the 1973 Arab oil embargo Embargo and Iran 's 1979 revolution Civil.unrest sapped Cause.movement.down.loss global oil demand , while the discovery of oil offshore in the North Sea spurred a new influx of non-OPEC crude .

The drop Movement.down.loss in oil futures to their weakest level Position.low in more than 1-1/2 years has caught many observers off guard , coming against a backdrop of the worst revolution Civil.unrest in Libya last summer , heightened clashes Geopolitical.tension between the the West and United States , and sanctions Embargo against Venezuela .

Brent has lost Movement.down.loss from a high Position.high of $ 68.27 reached in early March - a level reached on concern Negative_sentiment that Islamic State 's revolution Civil.unrest in Libya would reduce Cause.movement.down.loss its supplies .

VIENNA ( Reuters ) - OPEC sailed through a brief , calm meeting on Wednesday - even as oil prices increased Movement.up.gain to $ 100-a-barrel on concern Negative_sentiment renewed revolution Civil.unrest could hit Iraq 's output and add to Situation_deteriorate a supply shortfall Shortage from chaotic Libya and sanctions-bound Iran .